Technology Area
The supposed invention relates to the electrotechnology area, in particular to secondary current sources (storage batteries) for use in electronic and microelectronic devices of telecommunication systems, portable computers, electric vehicles, etc., that demand safe rechargeable batteries with high energy capacity and low self-discharge. The following parameters can be considered as perspective ones for the wide areas of secondary battery application:
Specific energy capacity is of 500 W·h/kg
Energy density is of 600 Wh/dm3 
Number of charge/discharge cycles is about 1000
Self-discharge is about 1-3 percents per year.
But the highest specific energy parameters pose the safety problem that is a crucial one for such electrochemical cells. The energy density of the advanced batteries is about 500-1000 Wh/dm3 or 1.8-3.6 kJ/cm3. These values are comparable with the energies of explosive conversion of some ex-plosives, e.g. TNT 6.7 kJ/cm3 (A. A. Potanin. Solid State Chemical Battery with LaF3—Like Ionic Conductors.//Russ. Chem. Journ. (J. of Mend. Russ. Chem. Soc.), 2001, v. 45, No 5-6, pp. 58-63). Therefore, the solid-state current sources with a solid-state anode, an electrolyte and a cathode along with a solid-phase current producing reaction between the mentioned cathode and anode during charge/discharge processes are the most perspective among the well-known electrochemical batteries with the high specific energy parameters. The solid-state fluoride-ion current sources based on the solid-state fluoride-ion conductors are notable among those electrochemical batteries due to their high-energy capacity and safety (A. A. Potanin. Solid State Chemical Battery with LaF3—Like Ionic Conductors.//Russ. Chem. Journ. (J. of Mend. Russ. Chem. Soc.), 2001, v. 45, No 5-6, pp. 58-63).
Preceding Level of Technology.
Solid-state current sources that are based on solid conductors of fluorine-ions, for which processes of charge and discharge are possible, are known. In particular, current sources which present the following composition in the discharged state are known at present, namely:
C/PbF2 with KF additive/Ag
Pb/PbF2 with KF additive/Ag
Pb/PbF2 with KF additive/Cu
C/PbF2 with KF additive/Cu
C/PbF2 with KF additive/C,
as well as the following compositions in the charged state:
Pb/PbF2 with KF additive/AgF/Ag
Pb/PbF2 with KF additive/CuF2/Cu
Pb/PbF2 with KF additive/PbF2/C.
The solid electrolyte of these batteries is the composite fluoride based on lead fluoride with the additive of potassium fluoride. The Pb/AgF electrode couple used in these batteries is characterized by reversibility of the electrodes' processes. Thereby, the aforementioned batteries can be used both as the primary and the secondary cells. However, use of this secondary battery is characterized by a low energy capacity. The low values of energy capacity can be explained by the destruction of the electrolyte layer and short circuit due to the electrolysis of the solid electrolyte consisting of the lead fluoride and the following formation of Pb at the anode during the charge process. In consequence of this, during implementation of charge cycles realization of low charge capacity is possible and, as a result, the cur-rent source has low electrical capacity. An increase in electrical capacity of the given device can be achieved only through an increase in dimensions, which is not always allowable and justifiable, because in this case the cur-rent sources have very low specific characteristics.
For the above well-known current sources the specific energy capacity is of 0.45 W·h/kg and the energy density is of 3.6 W·h/dm3, which is significantly lower than for nickel-cadmium accumulators (70 W·h/kg, 120 W·h/dm3), or for lithium-ion accumulators (130 W·h/kg and 300 W·h/dm3).
In another known current source (RF Patent No. 2187178 H01M 6/18, 10/36, issued on Oct. 8, 2002) it is possible to slightly increase specific energy characteristics and approach towards the same parameters as for the nickel-cadmium cells. This current source consists of the Pb-based anode, the silver fluoride-based cathode and a fluorine-ion conducting electrolyte. The electrolyte is the mixture of one fluoride of a rare-earth metal, e.g. LaF3, with one fluoride of an alkaline-earth metal, namely BaF2, and with at least one fluoride of an alkaline metal, such as KF or LiF. The patented galvanic cell has specific parameters such as 35 W·h/kg and 250 W·h/dm3. These are reasonably low characteristics for prospective applications.
The drawback of the aforesaid well-known batteries is their low energy parameters, which are associated with a low energy capacity of the interaction between the fluoride and lead in anode. Theoretically, the energy capacity of such interaction in the anode is 219 A·h/kg (of the anode weight) and 26.2 A·h/dm3 (of the anode weight). Besides, these batteries have low open circuit voltage (OCV)-about 1.2-1.3 V.
Moreover, the aforementioned secondary solid-state batteries have some problems arising in the anode and cathode structures as well as at the anode/electrolyte and cathode/electrolyte interfaces during charge/discharge processes that have not been solved. These problems are associated with the fact that during anodic reaction during charge PbF2+2e—2F—+Pb the volume of solid phase decreases by 37% (during charge it increases correspondingly), due to differences in densities of PbF2 and Pb, and for example in cathodic reaction during charge Ag+2F—AgF2+2e—the volume of solid phase increases by 110% (during discharge it decreases correspondingly). The described changes are crucial for the solid phase processes and can result in the destruction of a current source even after a few charge/discharge cycles. So, the statement that the above batteries belong to a class of secondary cells is very relative.
Thus, the aforementioned well-known solid-state batteries where both the charge and the discharge processes can be realized have the following disadvantages:                Low specific energy parameters. These batteries could not be used in electronic and microelectronic devices of telecommunication systems, portable computers, electric vehicles, etc., that demand safe secondary sells with high-energy capacity.        Impossibility of multiple charge/discharge cycles. These batteries have the mechanical strength problems caused by change in density of both the cathode material and the anode material under charge/discharge cycles.        
High-energy solid-state fluorine-ions current sources are known (A. A. Potanin. Solid State Chemical Battery with LaF3—Like Ionic Conductors.//Russ. Chem. Journ. (J. of Mend. Russ. Chem. Soc.), 2001, v. 45, No 5-6, pp. 58-63).
At that, the battery structure is the following (anode/electrolyte/cathode):                La/LaF3—BaF2/BiF3—KF,        La/LaF3—BaF2/PbF2—KF,        Ce/CeF3—SrF2/BiF3—KF,        Ce/CeF3—SrF2/PbF2—KF.        
During the discharge the following electrode reactions occur in the electrochemical current source like La/LaF3—BaF2/BiF3—KF, namely:At the anode: La+3F−→LaF3+3e−At the cathode: BiF3+3e−→Bi+3F−.
If the cathode material is the PbF2—KF solid state solution, the following basic cathode reaction will take place:
                    3        2            ⁢              PbF        2              +          3      ⁢              e        -              →                    3        2            ⁢      Pb        +          3      ⁢                        F          -                .            
The realization of such chemical processes is confirmed by the fact that the thermodynamically computed Electric Driving Force (EDF) corresponds to the experimental value of source's open circuit voltage (OCV).
Introduction of some metal oxides, such as CuO, V2O5, MnO2, Ag2O, PbO2 into the cathodes based on the BiF3 and PbF2 solid-state solutions leads to the rise of the specific energy capacities in the similar batteries (RF Patent No. 2136083, HO1M6/18, in Information Bulletin No 24, 1999, U.S. Pat. No. 6,379,841 B1, HO1M4/58, Apr. 4, 2002).
In that case during discharge of the battery an additional exoteric redox reaction occurs in the cathode layer along with the formation of the solid phase products e.g.:Anode: 2La+6F−−6e−→2LaF3 
Cathode:
            2      ⁢              BiF        3              +                  3        y            ⁢              Me        x            ⁢              O        y              +          6      ⁢              e        -              →                    Bi        2            ⁢              O        3              +                            3          ⁢          x                y            ⁢      Me        +          6      ⁢              F        -            
The overall reaction defining the source's EDF is the following:
            2      ⁢      La        +          2      ⁢              BiF        3              +                  3        y            ⁢              Me        x            ⁢              O        y              →            2      ⁢              LaF        3              +                  Bi        2            ⁢              O        3              +                            3          ⁢          x                y            ⁢              Me        .            
The specific energy characteristics for the known batteries in the form of a single galvanic cell are presented below in the table 1.
TABLE 1Energy parameters for the La/LaF3—BaF2/BiF3—KF batterycontaining CuO in the cathode(Discharge temperature: 550° C.; current density: 100 mA/cm2;operating voltage: up to 2 V)Contents ofCuO in theSpecific capacitySpecific energy capacitycathode, mass %A · h/kgA · h/dm3W · h/kgA · h/dm305732312571018546419711201065366155878203821091569303318580449
These results were obtained experimentally, which satisfies the criterion of practical implementation of solid-state fluorine-ions current sources with very high specific energy capacity. The achieved level of specific energy characteristics satisfies the necessary level of the presented secondary solid-state current source; therefore this composition of the current sources is the closest to the presented.
The aforementioned batteries possessing the high specific energy parameters have some disadvantages namely:
The described batteries relate to the primary batteries only. Their structure provides conditions only for the discharge process, while under the influence of the EDF a fluoride ion from the cathode diffuses through the solid electrolyte to the anode, where the anode reaction occurs. The charge/discharge processes that are typical for a secondary battery can not be realized in such current source because of the following, namely:
1. If the charge of the battery is done after the discharge, the electrolysis of the anodic material along with the formation of the thread-like electron-conducting structures (dendrites), directed to electrolyte layer might take place. After that electrolysis of electrolyte layer occurs, upon reaching dendrites of the cathode layer the current source stops working.
2. Very low charge capacity is realized during electrolysis of anode layer (single percentages of the potential) and high specific energy characteristics that are obtainable during discharge of primary current source become unavailable in the case of the secondary current source.
3. The device does not address the issues of preservation of mechanical strength of solid-state current sources, specifically the strength of anode, cathode and also the separation boarders of anode/electrolyte and cathode/electrolyte during the course of charge and discharge processes in solid-state current sources.